1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof. In this specification, a semiconductor device refers to any device capable of functioning with the use of semiconductor characteristics.
2. Description of the Related Art
In recent years, the information society has been increasingly developed, and the demand for higher speed, larger capacitance, smaller size, lighter weight, or the like of information communication equipment such as a personal computer or a mobile phone has been increased. With such a trend of the times, LSI (large scale integration) has been needed to be provided with higher integration, higher speed, and lower power consumption, which has resulted in essentially needing higher performance and miniaturization of each transistor for forming LSI.
Pattern diagrams of a conventional thin film transistor are FIGS. 12A to 12C. FIG. 12A is a top diagram of the thin film transistor, FIG. 12B is a cross-sectional diagram along a one-dotted dashed line O-P in FIG. 12A, and FIG. 12C is a cross-sectional diagram along a one-dotted dashed line Q-R in FIG. 12A. Note that, in FIG. 12A, a thin film and the like included in the thin film transistor are partially omitted.
As for the thin film transistor, an island-shaped semiconductor layer 9006 is provided over a substrate 9000 with a base insulating layer 9002 interposed therebetween. Over the semiconductor layer 9006, a conductive layer 9012 which functions as a gate electrode is formed with a gate insulating layer 9004 interposed therebetween. Further, the semiconductor layer 9006 includes a channel formation region 9008 which is formed in the region which overlaps with the conductive layer 9012 with the gate insulating layer 9004 interposed therebetween, and source and drain regions 9010. Further, an interlayer insulating layer 9014 is provided over the gate insulating layer 9004 and the conductive layer 9012, and conductive layers 9016 which function as source and drain electrodes are formed over the interlayer insulating layer 9014. The conductive layers 9016 are electrically connected to the semiconductor layer 9006.
In view of higher performance and miniaturization of a transistor, various structures have been considered for a thin film transistor. For example, in order to realize higher performance and miniaturization of a transistor, reduction in thickness of a gate insulating layer has been progressed.
For example, according to Reference 1 (Japanese Published Patent Application No. 2003-289079), ionized hydrogen is introduced into a semiconductor layer such that the surface of the semiconductor layer is subjected to ozone oxidation, whereby thinning of a gate insulating layer can he performed and a thin film transistor with good characteristics can be formed.